Low-water alarm



' May 24, 1927.

H. B. THURSTON LOW WATER ALARM Filed March 24,

Patented May 24, 1927.

UNITED STATES PATENT OFFICE.

LOW-WATER ALARM.

Application filed March 24, 1924. 7 Serial No.701,598.

This invention is in the nature of an improvement upon low water alarm devices for steam boilers, such as shown, described and 4 I ilar section taken on the line 3-3 of Fig. 1;

claimed in my prior application No. 643,512, filed June 5th, 1923, wherein a readily fusible material normally closes a conduit leading from the steam space within the boiler to a signal. v

' Theposition of the fusible material in the present device, as in the arrangement of the prior applications and similar devices, is such that should the water reach a dangerously low level, the lower conductivity of the surrounding steam will allow heat from 5 the fire box to be transmitted to the fusible material in suflicient degree to melt it per mitting the passage of steam through the opening, normally closed thereby, to operate the signal. Y

The essential'objects of the present invention are to provide greater simplicity in the construction of such low water alarms and to improve the methods of installation and inspection. More specifically, provide a means for carrying the fusible metal in a plug interposed between two' passages. so that it may be'readily accessible from the interior of the fire box and it will not be necessary, as in the device of the prior application, to remove anything but the protecting plug and the plug carrying the fusible closure.

Another specific object is to so arrange a simple signal operating steam pipe and passages leading thereto as to avoid drilling unnecessary openings in the boiler sheet or steam dome. A still further specific object is to arrange for mounting the fusible plug on the interior of the carrying member providing the portion of the steam passages from the boiler to support for the fusible plug shall be provided with openings large enough that they cannot be closed by the melted fusible metal,

and also so that the metal adjacent these openings may be hotter than that ofthe fusible plug itself.

Further objects and advantageous features of my invention will become apparent in the following description, with reference to the accompanying drawings. The essential characteristics of, the improvements embodied in the present invention are summarized in the claims.

In the drawings Fig, 1 is a side elevation partly in section of the alarm and connec- I desire to the signal, so that the tions from the boiler to the signal; Fig. 2 1s a transverse section taken substantially on the line 22 in Fig, 1; Fig. 3 is a sim- Fig. 4i is a fragmentary section showing a slightly modified form of the means for carrying the fusible plug and connections to the crown sheet.

In the drawings a portion of the crown sheet is indicated at 1 and a portion of the boiler roof sheet at 2. Between these, of course. is the usual steam spa-ce and below the crown sheet is the fire box. A suitable sleeve 5 is threaded into the crown sheet from within the fire box and from this sleeve rises a tubelO projecting outwardly from the roof sheet ofthe boiler and leading to and carrying a suitable signal 12.

sleeve '15 threaded into the sheet 2 provides for a suitable packing, embracing the tube and also provides in effect a steam dome 14cfrom which a communicating pipe 18 leads back to the fusible plug. This steam dome efiect whereby dry steam only'is admitted to the alarm without necessitating the provision of more than one opening in the boiler wall is more fully set out in a copending application filed by me July 18, 1924, Serial No. 726,711. The pipe 18 is suitably connected to a pipe leading through a suitable cap member to be later described, to within the tube 10. The sleeve 15 is shown as provided with an angular portion 16 and is provided with the usual packing gland 17 and nut '19.

The pipe 20, within the tube 10, extends downwardly and terminates within the sleeve 5 being threaded to an upward pro- 1ect-1on. rigid with the interior thereof, as

indicated at 24. A transverse wall formed in the sleeve 5 designated 25. is provided with a series of openings th'erethrough as at 2.6,

and an opening inside of the wall below the pro ection 24 is threaded to receive a plug having a central opening normally filled by the fusible material 32. This opening is preferably shown astapered and is provided with one or more grooves 37 to prevent downward movement of the material. under the pressure of the steam to which it is subjected until it melts (due to additional heatconducted thereto from the fire box temperature when the water in the boiler falls to a dangerously low level)- The sleeve 5 is threaded as at 33 to receive the threaded enlargement 34 of a plug 35 extending downwardly below the inner end of the sleeve 5 and having an enlargement 36 preferably closely fitting a counterbored portion of the lower end of the sleeve, thus effectually closing it at its lower end. The reduced portion shown between the enlargements of the, plug forms in effect an insulating space. This prevents the plug giving up too much heat to the sleeve at the point where the cooling efl ect of the crown sheet is effective. and at the same time pro tects the threads above from the destructive action of the fire in the fire box. An angular opening is shown in the lower end of the plug by which it may be turned. The upper face of the plug 35 is, preferably cupped as shown to form an enlarged recess which may hold all or a portion of the fused metal, in case it is not carried upwardly through the openings 26 by the flow of steam to the whistle.

The temperature'in the boiler adjacent the crown sheet. while the water is high enough to SllTl'OllDCltllQ greater portion of the sleeve 5. is such that the fusible material remains solid. Should the water in the boiler fall to a dangerously low level. for example below the engaging zone of the threads of the plug 34,, the heat conducted through the plug 34 and through the wall 2:") and plug 30 to the fusible material. 32 very quickly becomes suf icicnt to melt this fusible 1na-' terial. Steam from within the boiler will then pass through the space 14 between the sleeve and the tube 10, into the pipe 18 and down through the pipe 20, through the opening normally filled by the fusible material, and then upwardly through the openings 26, tube 10 and through a passage 38 thus sounding the signal 12.

At the joint between the passage and tube 10, is shown a fitting 4L0. threaded onto the upper end of the tube and tightly embracing the pipe 20. and having an upwardly sloping inner surface indicated at 41. providing a conical space forming a trapping chamber for any of the fusible material which may be carried upwardly by the steam. This prevents it clogging the passage to the whistle. i i

11 improvement in the present arrangement of the signal is the positioning of the whistle, shown with the opening thereof downwardlypto prevent the admission of moisture. such as when a locomotive is running in the rain. This is because if water enters the device and accumulates around. the fusible plug, it might tend to prevent the plug melting as quickly as it should to warrant safety.

A. modified. form shown in Figs 4 and 5 provides for more direct conduct of the heat to the plug carrying the fusible metal. In this case the plug 35 has the threaded enlargement 34- as before, but the upper face tudinal bore t5 are transverse openings 47 in the plug each the full size of the bore 45, and therefore, larger than the small end of the tapered openineoccupied by the fusi ble material.

The enlargement 36 of the plug preferably closely fits the cylindrical inner surface of the lower end of the sleeve 5 thus protecting the threads above. This engage ment is jn eferably well below the crown sheet so that heat be conducted through. the shank of the plug without being materially reduced by the cooling effect of the crown sheet. The lower end of the plug may be recessed or may have an angular projection, as shown. In this form, the heat of the fir. box is transmitted through the plug and, because of the close contact with the plug 30 directly to the fusible material bu while the water remains high enough to be above the zone of the fusible plug, its cooling effect is such as to prevent the melting of the fusible material. If. however, the water becomes sutliciently lowered that the heat passing up through the plug is not tel-zen away at the enlargement 3st and at the wall 25, the fusible material is melted and forced downwardly into the recess 46. This leaves the passa -'e open through the bore and openings 4;. ant S6,allowing the steam to pass to the alarm. 7

From the foregoing des "iption it will be seen that inspection and testing of the alarm device may be accomplished by rem ring plug 34 and then removing the plug 30. giving an opportunity to inpect the condition of the fusible material, and when the parts are thus opened, an air hose may be used to cause the signal to sound. assuring that the device is operative. The replacing of the parts is equally simple. f

Having thus described my invention, what I claim is:-

1. In a low water alarm for a boiler, the

combination of a conduit lee-uling to the exterior of the boiler and including a sleeve having threaded engagement with the crown sheet of the boiler. a pipe within said con duit. an inwardly extending portion of said sleeve having threaded engagement with said pipe, a passage through said inm extending portion allowing connminic from the pipe to the conduit. a threaded plug normally closing said communication lee and having an opening filled by fusible material, and another plug below the first, closin the lower end of said sleeve.

2; Ila a low water alarm, in combination with a pipe leading from the steam space of a boiler, a tube surrounding a portion of said pipe and leading to a signal, communication between said pipe and tube being in terrupted by a fusible material carriedv by a plug,-a transverse spider having an opening therethrough threaded to receive said plug and located adjacent the crown sheet, and removable means for closing the lower end of said tube.

3. A low water alarm for a boiler comp rising a pipe leading from the steam space of the boiler to a point adjacent the crown sheet, a sleeve having a spider to which said pipe is threaded the sleeve being threaded to the crown sheet, and a tube threaded to said sleeve forminga passage leading to the signal, means to afford communication between said pipe and passage, a removable plug having a fusible portion normally interrupting such communication, said plug being accessible from the inner end of the sleeve toward the interior of the fire box, and a closure normallyv protecting it and rendering effective the passage from the pipe to the tube, there being openings in said spider allowing the passage of steam therethrough, said spider serving to conduct the heat from the fire box to the fusible plug.

4. In combination with a boiler having a steam space and fire space separated by a crown sheet, two tubes one within the other, one communicating with the steam space and one adapted to communicate with a signal device, tubular. means secured to the crown sheet and to the said tubes and arranged to afford communication therebctween the arrangement comprising a perforated transverse member extending across the tubular means to which member the inner of the two tubes is fixed, a plug containing fusible material secured to the member and normally interrupting the communication, said plug being removable toward the tire space, and means closing communication between the said tubular means and the fire space, also removable toward the fire space.

5. In a device of the character described, the combination of means including a pipe and tube forming a passage from the steam space to a signal, said means also including a connecting member for the pipe and tube threaded into thecrown sheet and exposed to the fire, said connecting member being a threaded to said pipe and tube and having a perforated transverse portion completing a passage from the one to the other, a plug threaded into said portion normally closing said passage and carrying a fusible material, the connecting member having a threaded inward opening adapted to be leading within the roof sheet and secured to the crown sheet, a hollow member encircling the conduit in threaded engagementwith the roof sheet for rigidly supporting the conduit in place, a tube communicating with the hollow member and extending within the conduit for conveying steam thereto from the steam space, a normally closed connection between the end of said tube and the con duit, in proximity to the crown sheet, comprising a fusible plug, and an alarm device in communication with the conduit arranged to be actuated by steam from the tube when the plug is fused.

7. In a device of the character described, the combination of a conduit leading from the steam space to a signal and including a sleeve threaded to the wall of the fire box, a pipe threaded to said sleeve, said sleevehaving a transverse wall with openings therethrough, one being threaded to receive the pipe, a member carrying fusible material threaded into the same opening, the sleeve being threaded adjacent the connection with the fire box wall to receive a closure plug larger than the said member whereby both the plug and member may be removed from within the fire box.

8. In a device of the character described, the combination of tubular elements including two tubes forming a passage from the steam space to a signal, one of the said tubes being within another and terminating adjacent the crown sheet, a connecting tubular element threat ed to each tube and extending through the crown sheet and threaded thereto, a plug located within the connecting element and interrupting communication be tween the two tubes and having a fusibleportion occupying an opening therethrough, another plug threaded within the said elemen-tat a point on the steam space side of the crownzsheet, said latter plug having a recess to receive the fusible material when melted and having a reduced portion extending through the crown sheet toward the fire space and closely fitting said element to close the same a material distance below the crown sheet, and serving to conduct heat directly to the plug carrying the fusible material.

9. In a low water alarm the combination with a passage leading from the steam space,

including a pipe and a tube surrounding a portion of said pipe and communicating with a signal, a fusible material and a plug carrymg the fusible material located near the end of the pipe and arranged to interrupt communication between the pipe and tube, a wall portion receiving said plug and rigid with the tube and pipe and having openin therethrough, ren'iovable means closing the lower end of the tube said means being in engage-- ment with the plug and extending toward the tire space.

10. In a low ater alarm in combination a pipe leading from the steam space of a boiler to a point adjacent the crown sheet. a sleeve having an interior wall to which said pipe is threaded, the sleeve being threaded to the crown sheet, a tube connected to the sleeve and forming a passage leading: to the signal, a fusible plug carried by said wall to interrupt com nunicatiou between said pipe and passage, a removable plug threaded into the sleeve and extending into the tire box out of contact with the sleeve for a portion of its length, and closely littin r and closing, the lower end of the sleeve below he crown sheet.

11. In a low water alarn'r the combination of members forming a passage from the steam space to a signal and including an element adjacent the crown sheet in the nature ofa tube threaded to the crown sheet and having an interior wall. fusible material interrupting said passage carried by said wall, said element having a normally closed opening adjacent the fire space, and a member closing said opening and threaded to the interior of the element at a point above the crown sheet and in close engagement with the element at a point below the crown sheet and having, an intermediate reduced portion, whereby an air chamber is formed between the walls of said element and the last named member in the region of the crown sheet.

12. In alow water alarm the combination with pipes leading from the steam space to an alarm including on pipe within another terminating adjacent the wall of the lire box, a tubular element threaded through the wall of the fire box and to the outer tubular member, and having an interior member threaded to receive the inner tube, and also having openings providing a passage from one tube to the other, fusible material carried by said interior member and normally interrupting said passage, a plug closing the inner end 01 said element and extending into the tire box, said plug being threaded to the said element at a point on the steam space side of the wall of the tire box and engaging the member carrying the fusible material and having a reduced portion spaced apart from the tubular element for a distance above and below the said wall of the fire box. 7

1 In combination with a boiler having a root sheet and a crown sheet, a pair of tubes one within the other, means for supporting said tubes adjacent the crown sheet of the boiler whereby com'n'uinication is allorded from one tube to the other, and fusible material supported by said supporting means and arran retl to normally interrupt such communication a member surrounding the outer tube and secured to the root sheet, said member being separated from the outer tube tor a substantial distance above the root sheet to form in effect a steam dome, a tube eominunicating between this steam dome and the inner tube above the upper end of the outer tube, and means surmountingthe outer tube for laterally supporting the inner tube,

said last named means communicating with the interior ol said outer tube, and with a signal device. whereby when the fusible material melted by heat from the crown sheet. steam from the dome and inner tube travels alone the outer tube and through the said inner tube supporting means to actuate the a'arm,

14-. In a low water alarm for a boiler in combination. tubular means communicating with the steam space of the boiler and adapted to comnmnicate with a signal exteriorly thereof said means including a sleeve secured to the crown sheet, a plug-1- containing fusible material carried by the sleeve and being interposed in said tubular means to normally interrupt coi'nmunication from the steam space to the signal, and aplug' closing the sleeve and secured therewithin and extending toward the tire space, said plug beingin Contact with the sleeve above and below the crown sheet and separated therefrom opposite the crown sheet.-

In testimony whereof, I hereunto affix my signature.

HERMAl B. THURSTON. 

